An Empirical Method for the Determination of Elemental Components of Radiated Powers and Impurity Concentrations from VUV and XUV Spectral Features in Tokamak Plasmas

Abstract

The derivation of elemental components of radiated powers and impurity concentrations in bulk tokamak plasmas is complex, often requiring a full description of the impurity transport. A novel, empirical method, the Line Intensity Normalization Technique (LINT) has been developed on the JET (Joint European Torus ) tokamak to provide routine information about the impurity content of the plasma and elemental components of radiated power (Prad). The technique employs a few VUV and XUV resonance line intensities to represent the intrinsic impurity elements in the plasma. From a data base comprising these spectral features, the total bolometric measurement of the radiated power and the Zeff measured by visible spectroscopy, separate elemental components of Prad and Zeff are derived. The method, which converts local spectroscopic signals into global plasma parameters, has the advavtage of simplicity, allowing large numbers of pulses to be processed, and, in many operational modes of JET, is found to be both reliable and accurate. It relies on normalizing the line intensities to the absolute calibration of the bolometers and visible spectrometers, using coefficients independent of density and temperature. Accuracies of the order of +15% can be achieved for the elemental Prad components of the most significant impurities and the impurity concentrations can be determined to within +30%. Trace elements can be monitored, although with reduced accuracy. The present paper deals with limiter discharges, which have been the main application to date. As a check on the technique and to demonstrate the value of the LINT results, they have been applied to the transport modelling of intrinsic impurities carried out with the SANCO transport code, which uses atomic data from ADAS. The simulations provide independent confirmation of the concentrations empirically derived using the LINT technique. For this analysis, the simple case of the L-mode regime is considered, the chosen pulses ha

Additional information

Authors: JET (GB), JET Joint Undertaking, Abingdon (GB)

Bibliographic Reference: Article: An Empirical Method for the Determination of Elemental Components of Radiated Powers and Impurity Concentrations from VUV and XUV Spectral Features in Tokamak Plasmas, JET-P(1998)33, 1-30